The present invention relates to an automatic radioisotope filling apparatus for reducing the radiation exposure which the operator of the apparatus undergoes.
A drug labeled with a radioisotope (hereinafter referred to as a RI) (this drug is hereinafter referred to as a labeled drug), when injected into a human body, is selectively collected in a particular tissue or internal organ of the body, depending upon the type of labeled drug. Examination of the condition by an appropriate detector makes it possible to obtain the physiological or pathophysiological information of the tissue or internal organ in question.
Many nuclides are used as RIs for labeling. Of them, technetium 99m (Tc-99m) is used the most. Tc-99m is a daughter nuclide of Mo-99 and has a short half life of 6 hours. Therefore, Tc 99m is obtained, when required, in a form of a RI solution containing Tc-99m, from an apparatus generally called a technegenerator (RI generator) which contains Mo-99 and its daughter nuclide, namely, Tc 99m and from which only Tc-99m can be taken out selectively. As a matter of course, the radioactive intensity per unit volume, i.e. specific radioactivity of the RI solution taken out from the technegenerator varies by the time period since the production of the technegenerator or by the producer. Accordingly, the specific radioactivity of the RI solution must be measured correctly in order to prepare a labeled drug of a desired amount. Further, it is necessary in some cases to dilute the RI solution with a physiological saline solution to adjust the specific radioactivity of the former to a desired level.
Preparation of a labeled drug has been manually conducted by measuring the radioactive intensity of a RI solution contained in a RI vial, separately measuring the amount of the RI solution visually in most cases, calculating the specific radioactivity of the solution from its radioactive intensity and amount both obtained above, transferring required amounts of the RI solution and a physiological saline solution to a vial containing a drug by means of a syringe or the like, and effecting stirring.
Such manual handling of RI has been defective in that the operator undergoes a large radiation exposure as a result of such an operation over a long period of time and may possibly have a serious hazard.
In order to improve the manual handling of RI and thereby to reduce the radiation exposure which the operator undergoes, the present applicant proposed an automatic RI filling apparatus which can solve the above problems (reference is made to U.S. Pat. No. 4,853,546.
This automatic RI filling apparatus comprises:
(a) a RI vial containing a RI solution,
(b) a saline vial containing a physiological saline solution,
(c) a dilution vial to which a predetermined amount of the RI solution and a predetermined amount of the physiological saline solution are to be transferred to prepare a diluted RI solution,
(d) a radiation detector for measuring the radioactive intensity of the diluted RI solution in the dilution vial, and
(e) a plurality of label vials containing a drug to be labeled, wherein the diluted RI solution prepared in the dilution vial is automatically transferred to the label vials containing a drug to prepare a labeled drug.
The automatic RI filling apparatus enabled the significant reduction of the accumulated radiation exposure which the operator undergoes during the preparation of a labeled drug.
In the above automatic RI filling apparatus, however, there is a problem that the operator may undergo radiation when the operator opens the opening of a vial shield containing a label vial to take out the label vial for exchange, etc., because the opening is directed upright. Further in the automatic RI filling apparatus, each label vial is stirred after the diluted RI solution has been transferred to all the label vials; therefore, in the label vial to which the diluted RI solution has been transferred at first, the mixing of the diluted RI solution and the drug solution is insufficient until the transfer of the diluted RI solution to the other label vials is completed and the stirring of all the label vials is started; as a result, there occurs a reduction in labeling efficiency.
Further in the automatic RI filling apparatus, the RI solution contained in the RI vial is produced ahead of time by a generator (e.g. technegenerator) which milks a RI (e.g. technetium) to produce a RI solution, and then transferred to the RI vial; this production of a RI solution is effected by means of a vacuum vial, and suction lasts until the vacuum in the vacuum vial disappears; as a result, the RI solution becomes surplus when labeling requires a small amount of the RI solution. In some cases, the operator quits the collection of the RI solution in the middle: this is done based mainly on the operator's intuition; consequently, the amount of the RI solution collected and the radioactivity of the RI solution differ from those required.
Hitherto, there has existed no such automatic RI filling apparatus that has a generator incorporated therein and can integrally effect milking of RI, metering of the resulting RI solution, transferring of the solution and labeling of drug with the solution.
The above mentioned automatic RI filling apparatus has been found to further have the following problem. When a solution is suction-transferred between the vials by a metering means (e.g. syringe) or when a solution in the tube is discharged, a small volume of the RI solution adheres to the front end of the syringe piston and, in the subsequent transferring operation, this RI solution causes mixing with the RI solution to be newly transferred. The solution transferred into the tube cannot be completely withdrawn from the tube. The solution remains in the tube in the form of droplets adhering to the inner wall of the tube. As a result of these inconveniences, it is impossible to transfer the RI solution to the dilution vial or each label vial in an amount of a precisely known radioactivity.